In U.S. Pat. No. 2,757,261, issued July 31, 1956, to Harry J. Lingal, Thomas E. Browne, Jr., and Albert P. Strom, there are illustrated and described various types of circuit-interrupting structures, of both the puffer-type, and also the gas-storage type, utilizing as the arc-extinguishing gas sulfur-hexafluoride (SF.sub.6) gas under suitable pressures. This patent, additionally, suggests the admixtures of other gases, for example, stating that while the inventors have secured the best results with an arc-interrupting gas composed of sulfur-hexafluoride (SF.sub.6) alone, small quantities of one or more other gases may be admixed therewith, over 50% of the gas, preferably, being sulfur-hexafluoride gas. Moreover, the aforesaid U.S. Pat. No. 2,757,261 suggests, as examples of such added gases, air, nitrogen, hydrogen, argon, helium, and carbon dioxide gases. Moreover, said patent, on column 16 thereof, states that in FIG. 19 of said patent the interrupting performance of a mixture of 50% air and 50% sulfur-hexafluoride gas at two voltages, namely, 2,300 volts, and 13,800 volts, compared with the performance of 100% sulfur-hexafluoride gas at 2,300 volts and 13,800 volts. From these curves, the aforesaid patent states that it is apparent that even with air mixed with an equal amount with the sulfur-hexafluoride gas, nevertheless beneficial results are obtained, and the performance is considerable better than that with 100% air.
It has been well known by those skilled in the art that certain manufacturing companies, such as the Westinghouse Electric Corporation and the ITE Imperial Company, have manufactured commercial circuit-interrupters, utilizing exclusively sulfur-hexafluoride (SF.sub.6) gas, as not only the arc-extinguishing medium, but, in certain instances, utilizing the same (SF.sub.6) gas, namely sulfur-hexafluoride gas, as the operating medium to effect operation of the separable contact structure as well as effecting an arc-extinguishing gas flow to extinguish the arc. An example of a high-power piece of equipment utilizing sulfur-hexafluoride gas to advantage, utilizing a double break within a single circuitbreaker module, reference may be had to U.S. Pat. No. 3,291,947, issued Dec. 13, 1966, to R. C. Van Sickle and assigned to the assignee of the present invention.